diff --git a/ovn/lib/automake.mk b/ovn/lib/automake.mk
index 6178fc2..c1d37c5 100644
--- a/ovn/lib/automake.mk
+++ b/ovn/lib/automake.mk
@@ -17,7 +17,9 @@ ovn_lib_libovn_la_SOURCES = \
 	ovn/lib/ovn-util.c \
 	ovn/lib/ovn-util.h \
 	ovn/lib/logical-fields.c \
-	ovn/lib/logical-fields.h
+	ovn/lib/logical-fields.h \
+	ovn/lib/inc-proc-eng.c \
+	ovn/lib/inc-proc-eng.h
 nodist_ovn_lib_libovn_la_SOURCES = \
 	ovn/lib/ovn-nb-idl.c \
 	ovn/lib/ovn-nb-idl.h \
diff --git a/ovn/lib/inc-proc-eng.c b/ovn/lib/inc-proc-eng.c
new file mode 100644
index 0000000..54c7fd6
--- /dev/null
+++ b/ovn/lib/inc-proc-eng.c
@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) 2018 eBay Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+
+#include <errno.h>
+#include <getopt.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "openvswitch/dynamic-string.h"
+#include "openvswitch/hmap.h"
+#include "openvswitch/vlog.h"
+#include "inc-proc-eng.h"
+
+VLOG_DEFINE_THIS_MODULE(inc_proc_eng);
+
+static bool engine_force_recompute = false;
+
+void
+engine_set_force_recompute(bool val)
+{
+    engine_force_recompute = val;
+}
+
+void
+engine_init(struct engine_node *node)
+{
+    for (size_t i = 0; i < node->n_inputs; i++) {
+        engine_init(node->inputs[i].node);
+    }
+    if (node->init) {
+        node->init(node);
+    }
+}
+
+void
+engine_cleanup(struct engine_node *node)
+{
+    for (size_t i = 0; i < node->n_inputs; i++) {
+        engine_cleanup(node->inputs[i].node);
+    }
+    if (node->cleanup) {
+        node->cleanup(node);
+    }
+}
+
+void
+engine_run(struct engine_node *node, uint64_t run_id)
+{
+    if (node->run_id == run_id) {
+        return;
+    }
+    node->run_id = run_id;
+
+    if (node->changed) {
+        node->changed = false;
+    }
+    if (!node->n_inputs) {
+        node->run(node);
+        VLOG_DBG("node: %s, changed: %d", node->name, node->changed);
+        return;
+    }
+
+    size_t i;
+
+    for (i = 0; i < node->n_inputs; i++) {
+        engine_run(node->inputs[i].node, run_id);
+    }
+
+    bool need_compute = false;
+    bool need_recompute = false;
+
+    if (engine_force_recompute) {
+        need_recompute = true;
+    } else {
+        for (i = 0; i < node->n_inputs; i++) {
+            if (node->inputs[i].node->changed) {
+                need_compute = true;
+                if (!node->inputs[i].change_handler) {
+                    need_recompute = true;
+                    break;
+                }
+            }
+        }
+    }
+
+    if (need_recompute) {
+        VLOG_DBG("node: %s, recompute (%s)", node->name,
+                 engine_force_recompute ? "forced" : "triggered");
+        node->run(node);
+    } else if (need_compute) {
+        for (i = 0; i < node->n_inputs; i++) {
+            if (node->inputs[i].node->changed) {
+                VLOG_DBG("node: %s, handle change for input %s",
+                         node->name, node->inputs[i].node->name);
+                if (!node->inputs[i].change_handler(node)) {
+                    VLOG_DBG("node: %s, can't handle change for input %s, "
+                             "fall back to recompute",
+                             node->name, node->inputs[i].node->name);
+                    node->run(node);
+                    break;
+                }
+            }
+        }
+    }
+
+    VLOG_DBG("node: %s, changed: %d", node->name, node->changed);
+
+}
+
diff --git a/ovn/lib/inc-proc-eng.h b/ovn/lib/inc-proc-eng.h
new file mode 100644
index 0000000..3e0ec16
--- /dev/null
+++ b/ovn/lib/inc-proc-eng.h
@@ -0,0 +1,224 @@
+/*
+ * Copyright (c) 2018 eBay Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef INC_PROC_ENG_H
+#define INC_PROC_ENG_H 1
+
+/* The Incremental Processing Engine is a framework for incrementally
+ * processing changes from different inputs. The main user is ovn-controller.
+ * To compute desired states (e.g. openflow rules) based on many inputs (e.g.
+ * south-bound DB tables, local OVSDB interfaces, etc.), it is straighforward
+ * to recompute everything when there is any change in any inputs, but it
+ * is inefficient when the size of the input data becomes large. Instead,
+ * tracking the changes and update the desired states based on what's changed
+ * is more efficient and scalable. However, it is not straighforward to
+ * implement the change-based processing when there are a big number of
+ * inputs. In addition, what makes it more complicated is that intermediate
+ * results needs to be computed, which needs to be reused in different part
+ * of the processing and finally generates the final desired states. It is
+ * proved to be difficult and error-prone to implement this kind of complex
+ * processing by ad-hoc implementation.
+ *
+ * This framework is to provide a generic way to solve the above problem.
+ * It does not understand the processing logic, but provides a unified way
+ * to describe the inputs and dependencies clearly, with interfaces for
+ * users to implement the processing logic for how to handle each input
+ * changes.
+ *
+ * The engine is composed of engine_nodes. Each engine_node is either
+ * an input, an output or both (intermediate result). Each engine node
+ * maintains its own data, which is persistent across interations. Each node
+ * has zero to ENGINE_MAX_INPUT inputs, which creates a DAG (directed
+ * acyclic graph). For each input of each engine_node, there is a
+ * change_handler to process changes of that input, and update the data
+ * of the engine_node. Then the user can simply call the run() method
+ * of the engine so that the processing will happen in the order according
+ * to the dependencies defined and handle the changes incrementally.
+ *
+ * While the more fine-grained dependencies and change-handlers are
+ * implemented, the more efficient the processing will be, it is not
+ * realistic to implement all change-processing for all inputs (and
+ * intermediate results). The engine doesn't require change-handler to be
+ * implemented for every input of every node. Users can choose to implement
+ * the most important change-handlers (for the changes happens most
+ * frequently) for overall performance. When there is no change_handler
+ * defined for a certain input on a certain engine_node, the run() method
+ * of the engine_node will be called to fall-back to a full recompute
+ * against all its inputs.
+ */
+
+#define ENGINE_MAX_INPUT 256
+
+struct engine_node;
+
+struct engine_node_input {
+
+    /* the input node */
+    struct engine_node *node;
+
+    /* Change handler for changes of the input node. The changes may need to be
+     * evaluated against all the other inputs. Returns:
+     *  - true: if change can be handled
+     *  - false: if change cannot be handled (indicating full recompute needed)
+     */
+    bool (*change_handler)(struct engine_node *node);
+};
+
+struct engine_node {
+
+    /* A unique id to distinguish each iteration of the engine_run(). */
+    uint64_t run_id;
+
+    /* A unique name for each node */
+    char* name;
+
+    /* Number of inputs of this node */
+    size_t n_inputs;
+
+    /* Inputs of this node */
+    struct engine_node_input inputs[ENGINE_MAX_INPUT];
+
+    /* Data of this node. It is vague and interpreted by the related functions.
+     * The content of the data should be changed only by the change_handlers
+     * and run() function of the current node. Users should ensure that the
+     * data is read-only in change-handlers of the nodes that depends on this
+     * node. */ 
+    void *data;
+
+    /* Whether the data is changed in the last engine run */
+    bool changed;
+
+    /* Context data for the engine processing, such as OVSDB IDLs */
+    void *context;
+
+    /* Method to initialize data. It may be NULL. */
+    void (*init)(struct engine_node *node);
+
+    /* Method to clean up data. It may be NULL. */
+    void (*cleanup)(struct engine_node *node);
+
+    /* Fully processing all inputs of this node and regenerate the data
+     * of this node */
+    void (*run)(struct engine_node *node);
+};
+
+/* Initialize the data for the engine nodes recursively. It calls each node's
+ * init() method if not NULL. It should be called before the main loop. */
+void
+engine_init(struct engine_node *node);
+
+/* Execute the processing recursively, which should be called in the main
+ * loop. */
+void
+engine_run(struct engine_node *node, uint64_t run_id);
+
+/* Clean up the data for the engine nodes recursively. It calls each node's
+ * cleanup() method if not NULL. It should be called before the program
+ * terminates. */
+void
+engine_cleanup(struct engine_node *node);
+
+/* Get the input node with <name> for <node> */
+static inline struct engine_node *
+engine_get_input(const char *input_name, struct engine_node *node)
+{
+    size_t i;
+    for (i = 0; i < node->n_inputs; i++) {
+        if (!strcmp(node->inputs[i].node->name, input_name)) {
+            return node->inputs[i].node;
+        }
+    }
+    return NULL;
+}
+
+/* Add an input (dependency) for <node>, with corresponding change_handler,
+ * which can be NULL. If the change_handler is NULL, the engine will not
+ * be able to process the change incrementally, and will fall back to call
+ * the run method to recompute */
+static inline void
+engine_add_input(struct engine_node *node, struct engine_node *input,
+    bool (*change_handler)(struct engine_node *node))
+{
+    ovs_assert(node->n_inputs < ENGINE_MAX_INPUT);
+    node->inputs[node->n_inputs].node = input;
+    node->inputs[node->n_inputs].change_handler = change_handler;
+    node->n_inputs ++;
+}
+
+/* Force the engine to recompute everything if set to true. It is used
+ * in circumstances when we are not sure there is change or not, or
+ * when there is change but the engine couldn't be executed in that
+ * iteration, and the change can't be tracked across iterations */
+void
+engine_set_force_recompute(bool val);
+
+/* Macro to define an engine node */
+#define ENGINE_NODE(NAME, NAME_STR, CTX) \
+    struct engine_node en_##NAME = { \
+        .name = NAME_STR, \
+        .data = &ed_##NAME, \
+        .context = CTX, \
+        .init = NAME##_init, \
+        .run = NAME##_run, \
+        .cleanup = NAME##_cleanup, \
+    };
+
+/* Macro to define member functions of an engine node which represents
+ * a table of OVSDB */
+#define ENGINE_FUNC_OVSDB(DB_NAME, TBL_NAME, IDL) \
+static void \
+DB_NAME##_##TBL_NAME##_run(struct engine_node *node) \
+{ \
+    static bool first_run = true; \
+    if (first_run) { \
+        first_run = false; \
+        node->changed = true; \
+        return; \
+    } \
+    struct controller_ctx *ctx = (struct controller_ctx *)node->context; \
+    if (DB_NAME##rec_##TBL_NAME##_track_get_first(ctx->IDL)) { \
+        node->changed = true; \
+        return; \
+    } \
+    node->changed = false; \
+} \
+static void (*DB_NAME##_##TBL_NAME##_init)(struct engine_node *node) \
+            = NULL; \
+static void (*DB_NAME##_##TBL_NAME##_cleanup)(struct engine_node *node) \
+            = NULL;
+
+/* Macro to define member functions of an engine node which represents
+ * a table of OVN SB DB */
+#define ENGINE_FUNC_SB(TBL_NAME) \
+    ENGINE_FUNC_OVSDB(sb, TBL_NAME, ovnsb_idl)
+
+/* Macro to define member functions of an engine node which represents
+ * a table of open_vswitch DB */
+#define ENGINE_FUNC_OVS(TBL_NAME) \
+    ENGINE_FUNC_OVSDB(ovs, TBL_NAME, ovs_idl)
+
+/* Macro to define an engine node which represents a table of OVN SB DB */
+#define ENGINE_NODE_SB(TBL_NAME, TBL_NAME_STR, CTX) \
+    void *ed_sb_##TBL_NAME; \
+    ENGINE_NODE(sb_##TBL_NAME, TBL_NAME_STR, CTX)
+
+/* Macro to define an engine node which represents a table of open_vswitch
+ * DB */
+#define ENGINE_NODE_OVS(TBL_NAME, TBL_NAME_STR, CTX) \
+    void *ed_ovs_##TBL_NAME; \
+    ENGINE_NODE(ovs_##TBL_NAME, TBL_NAME_STR, CTX)
+
+#endif /* ovn/lib/inc-proc-eng.h */
